Unconventional magnetic states and defects

This thesis explores unconventional magnetic structures with potential applications in spintronics and magnetic memory devices. We study the chiral frustrated antiferromagnet, Ba3TaFe3Si2O14, where we find a stable three-dimensional Skyrmion. This novel topological defect is a compact magnetic particle in three spatial dimensions, distinct from the conventional two-dimensional (2D) Skyrmion strings and closely related to the Shankar monopole in superfluid 3He-A and meson hedgehog in the Skyrme model of baryons. The centrosymmetric ferromagnet SrRuO3 shows 2D Skyrmion lattices stable over a wide parameter range and resilient against tilted magnetic fields. Our model that takes into account magnetodipolar interactions and high-order magnetic anisotropy of Ru spins explains the stability. We derive anisotropic interactions between Cr spins in CrI3 resulting from the strong spin-orbit coupling in iodine ligand ions, which explains unusual magnetic properties and magnon spectrum of this van der Waals magnet. We also explain sharp electric polarization peaks observed in the ferrimagnetic material Fe_{2−x}Zn_{x}Mo{_3}O{_8} at magnetization reversals by the intervention of the metastable antiferromagnetic state. These findings deepen our understanding of complex interactions in strongly-correlated electron systems, offering insights for future advancements in this field.